Notes on the above:1. Collect multiple examples of each expression, from multiple people.2. This is largely an image processing step. Do not neglect it: Doing it well can help a great deal down the line.3. Be creative in constructing features: This step can make the classifiers job much easier, if done well.4. This step will include the task of feature selection. Sometimes less is more: You will likely want to prune the features which are ultimately fed to the classifier, based on experimentation.5. Test on different people than are used for training the classifier.6. Do not forget this step!